The present invention relates to a touch-sensitive interface with shell mounting, touch-sensitive shell, and mechanical stress sensors.
An application outlined is the use of mechanical stress sensors, in particular, capacitive sensors, to make any surface touch-sensitive, whatever the material thereof (subject to it having elastic properties) and whatever the shape thereof (flat or embossed), the size thereof and the arrangement (horizontal, tilted or vertical).
Currently, the technologies used are mainly deploying a capacitive film on the shell surface to make it touch-sensitive, or placing an infrared frame around this surface. In the first case, illustrated, for example, by the patent application WO 2011/098854 A1, a plastic film wherein an electrical network connected to a calculation unit is embedded, extends over the surface. At the time of touching with a finger, the capacity measured is locally impeded, which enables the touch to be localized. But this technology is detrimental to the transparency of the surface whereon the film meshed with electrical wires is deployed, and deploying such a plastic film on an embossed surface can quickly prove to be problematic. In the second case, the frame is composed of emitting and receiving infrared light-emitting diodes arranged respectively horizontally and vertically opposite, so as to generate a surface grid pattern. When a finger or any other object cuts the horizontal and vertical beams, it is localized. However, this technology is very sensitive to sunlight, which is full of infrared rays, as well very sensitive to the environment (dirt). In addition, the surface must be flat. Moreover, in the two above-mentioned cases, the actual cost is high and quickly increases according to the size of the surface to make touch-sensitive. If this actual cost is wanted to be reduced, at the same time, the performance of the touch-sensitive interface is very substantially reduced.
Other technologies used are based on the propagation of acoustic waves, like for example, in the patent application US 2009/0116339 A1. But these technologies are sensitive to the environment, in particular, to temperature, and can require to be obligatorily learned about before they are used. In addition, the need to have to transmit an energy to the touch-sensitive interface from a touch to detect limits the possibilities of interpreting this touch. Moreover, the complexity of the learning quickly increases according to the size of the surface to make touch-sensitive.
Another solution is thus to arrange a certain number of mechanical stress sensors against the shell to make touch-sensitive, regardless of the size thereof and to apply a method based on a measurement of the respective stresses exerted on each sensor at the time of a touch to deduct from it, by barycentric calculation, the touch localization. Such a method is, for example, disclosed in the U.S. Pat. No. 3,657,475. A minimum of two sensors is necessary for a one-dimensional touch localization in relation to an axis. A minimum of three sensors is necessary for a two-dimensional localization, knowing that four sensors arranged in the four corners of a rectangular, flat shell enable to obtain satisfactory results with a good stability of the unit.
The U.S. Pat. No. 3,657,475 discloses four sensors interposed between a fixed mounting and a touch-sensitive surface at the four corners of the latter. These sensors are stress gauges or piezoelectric sensors. They must, on the one hand, support the out of charge weight of the touch-sensitive surface and, on the other hand, remain sensitive to touches of which the force or pressure is added to the weight of this touch-sensitive surface. The force of the touch cannot therefore be too low in relation to the weight of the surface to not lead to sensitivity problems as well as problems with precision. In addition, the sensors used in this document are quite expensive and piezoelectric sensors, in particular, are sensitive to temperature variations.
For these reasons, the invention is more specifically based on a touch-sensitive shell interface, against which mechanical stress sensors are arranged, for example, capacitive sensors, which are known to be cheap.
But in a context of a touch-sensitive surface sensitive to touches, capacitive sensors themselves can raise sensitivity or precision problems such as those mentioned above. In particular, the stress measured by the capacitive sensors is normal to the surface of the shell. It is therefore a function of tilting the capacitive sensors and can strongly vary during use, if the touch-sensitive shell against which the capacitive sensors are arranged changes tilt.
That is the reason why a solution based on means for mechanical stress compensation equipped with adjustable counterweights is proposed in the patent FR 3 003 030 B1. Such a mechanism protects the capacitive sensors against tilt changes, also improving the precision of their measurements.
However, this does not completely solve the problem raised by increased shear stress forces that the sensors are subjected to when the tilt increases, and in particular, when the interactive shell is a vertical partition. In addition, such a mechanism remains excessively sensitive to the conditions at the localized limits at the periphery of the interactive shell, in particular, the peripheral conditions thereof of attachment to or housing in a mounting. Finally, this mechanism is quite complex, therefore expensive.
In the patent EP 0 531 815 B1, recovering tangential shear stress forces in a vertical position of a touch-sensitive plate is ensured using attachment strips. But there again, the mechanism proposed remains too sensitive to the peripheral conditions of attaching the touch-sensitive plate to a mounting.